Magnetic power transmission utilizing phased transmitter coil arrays and phased receiver coil arrays

ABSTRACT

An improved wireless transmission system for transferring power over a distance. The system includes a transmitter generating a magnetic field and a receiver for inducing a voltage in response to the magnetic field. In some embodiments, the transmitter can include a plurality of transmitter resonators configured to transmit wireless power to the receiver. The transmitter resonators can be disposed on a flexible substrate adapted to conform to a patient. In one embodiment, the polarities of magnetic flux received by the receiver can be measured and communicated to the transmitter, which can adjust polarities of the transmitter resonators to optimize power transfer. Methods of use are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/676,723, filed on Jul. 27, 2012, titled “Magnetic Power TransmissionUtilizing Phased Transmitter Coil Arrays and Phased Receiver CoilArrays”, U.S. Provisional Application No. 61/790,795, filed on Mar. 15,2013, titled “Magnetic Power Transmission Utilizing Phased TransmitterCoil Arrays and Phased Receiver Coil Arrays”, and U.S. ProvisionalApplication No. 61/676,656, filed on Jul. 27, 2012, titled “ResonantPower Transmission Coils and Systems”.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

FIELD

This disclosure relates generally to methods and apparatus fortransmitting and receiving power wirelessly, and in various respects,mechanical circulatory support.

BACKGROUND

Powered devices need to have a mechanism to supply power to theoperative parts. Typically systems use a physical power cable totransfer energy over a distance. There has been a continuing need forsystems that can transmit power efficiently over a distance withoutphysical structures bridging the physical gap.

Systems and methods that supply power without electrical wiring aresometimes referred to as wireless energy transmission (WET). Wirelessenergy transmission greatly expands the types of applications forelectrically powered devices. One such example is the field ofimplantable medical devices. Implantable medical devices typicallyrequire an internal power source able to supply adequate power for thereasonable lifetime of the device or an electrical cable that traversesthe skin. Typically an internal power source (e.g., battery) is feasiblyfor only low power devices like sensors. Likewise, a transcutaneouspower cable significantly affects quality of life (QoL), infection risk,and product life, among many drawbacks.

More recently there has been an emphasis on systems that supply power toan implanted device without using transcutaneous wiring. This issometimes referred to as a Transcutaneous Energy Transfer System (TETS).Frequently energy transfer is accomplished using two magneticallycoupled coils set up like a transformer so power is transferredmagnetically across the skin. Conventional systems are relativelysensitive to variations in position and alignment of the coils. In orderto provide constant and adequate power, the two coils need to bephysically close together and well aligned.

Existing systems that transmit power wirelessly based on magnetic fieldstypically operate either in the near-field only, where the separation ofthe transmitter and receiver coils is less than the dimension of thecoils, or in mid-range, where the separation is comparable to the coildimensions, but then only with single a transmitter and a singlereceiver coil. Single-transmitter-coil, single-receiver-coil systems aresusceptible to a loss in power transmission if the receiver coil isoriented such that no magnetic fields lines emanating from thetransmitter coil passes through the receiver coil, e.g., if a flatreceiver coil is oriented with its normal perpendicular to the magneticfield lines.

SUMMARY OF THE DISCLOSURE

A wireless power transfer system is provided, comprising a flexiblesubstrate adapted to conform to the body of a patient, a firsttransmitter resonator disposed on the flexible substrate, a secondtransmitter resonator disposed on the flexible substrate, the secondtransmitter resonator being in electronic communication with the firsttransmitter resonator; a receiver resonator; and a transmit controllerconfigured to drive the first and second transmitter resonators todeliver wireless energy to the receiver resonator.

In some embodiments, the flexible substrate comprises a flexible fabric.In other embodiments, the flexible substrate is a material selected fromthe group consisting of Kapton, a polymide film, a polyester film, acloth, and a rubber.

In one embodiment, the flexible substrate is covered with a padding tobetter match a contour of the body.

In some embodiments, the second transmitter resonator is drivenout-of-phase from the first transmitter resonator.

In one embodiment, the first and second resonators coils aresubstantially rigid.

In some embodiments, the transmit controller is configured to operate ina test mode to drive the first transmitter resonator individually whilea receive controller in the receiver resonator is configured to record apolarity of the magnetic flux received from the first transmitterresonator.

In another embodiment, the transmit controller is further configured todrive the second transmitter resonator individually while the receivecontroller in the receiver resonator is configured to record a polarityof the magnetic flux received from the second transmitter resonator.

In some embodiments, the receive controller is configured to communicatethe measured polarity of the magnetic flux received from the firsttransmitter resonator to the transmit controller, and the transmitcontroller is configured to adjust transmission of power from the firsttransmitter resonator based on the recorded polarity.

In one embodiment, the receive controller is configured to communicatethe measured polarity of the magnetic flux received from the secondtransmitter resonator to the transmit controller, and the transmitcontroller is configured to adjust transmission of power from the secondtransmitter resonator based on the measured polarity.

A method of adjusting wireless power transmission in a TET system isprovided, comprising the steps of transmitting power from a firsttransmitter resonator external to a patient to a receiver resonatorimplanted within the patient, measuring a first polarity of magneticflux received by the receiver resonator, transmitting power from asecond transmitter resonator external to the patient to the receiverresonator implanted within the patient, measuring a second polarity ofmagnetic flux received by the receiver resonator, communicating themeasured first and second polarities from the receiver resonator to acontroller of the first and second transmitter resonators; and adjustingtransmission of power from the first and second transmitter resonatorsbased on the measured first and second polarities.

In some embodiments, the adjusting step comprises reversing a polarityof the first transmitter resonator.

In other embodiments, the adjusting step comprises reversing a polarityof the second transmitter resonator.

In some embodiments, the adjusting step comprises turning off the firsttransmitter resonator.

In one embodiment, the adjusting step comprises turning off the secondtransmitter resonator.

In some embodiments, the adjusting step comprises adjusting a polarityof one or more of the first and second transmitter resonators tomaximize power received by the receiver resonator.

A wireless power transmitter is also provided, comprising coil circuitryincluding at least two transmit resonators, and driver circuitryincluding a voltage source, the driver circuitry configured to excitethe coil circuitry to transmit wireless power from the at least twotransmit resonators to a receiver.

In one embodiment, the coil circuitry includes four transmit resonators.

In another embodiment, the at least two transmit resonators comprisefour resonators arranged in a 2×2 array.

In some embodiments, the transmit resonators are operated out of phase.

In other embodiments, the transmit resonators are operated in phase.

In one embodiment, at least one of the transmit resonators is operatedin phase and at least one of the transmit resonators is operated out ofphase.

A wireless power transfer system is provided, comprising first andsecond transmitter resonators configured to transmit wireless power to areceiver resonator implanted within a patient, a receive controllerconfigured to measuring first and second polarities of magnetic fluxreceived by the receiver resonator from the first and second transmitterresonators, respectively, the receive controller configured tocommunicate the measured first and second polarities to a transmitcontroller of the first and second transmitter resonators, the transmitcontroller configured to adjust transmission of power from the first andsecond transmitter resonators to the receiver resonator based on themeasured first and second polarities to maximize power transfer.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe claims that follow. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 illustrates a basic wireless power transfer system.

FIG. 2 illustrates the flux generated by a pair of coils.

FIGS. 3A-3B illustrate the effect of coil alignment on the couplingcoefficient.

FIG. 4 illustrates a resonator with multiple coils.

FIGS. 5A-5C illustrate various in-phase and out-of-phase orientations ofmultiple coil systems.

FIG. 6 illustrates circuitry for a single coil transmitter and singlecore receiver.

FIG. 7 illustrates circuitry for a dual coil transmitter.

FIG. 8 illustrates circuitry for a quad coil transmitter.

FIGS. 9A-9C illustrate a resonator with multiple flexibly connectedrigid coils.

DETAILED DESCRIPTION

In the description that follows, like components have been given thesame reference numerals, regardless of whether they are shown indifferent embodiments. To illustrate an embodiment(s) of the presentdisclosure in a clear and concise manner, the drawings may notnecessarily be to scale and certain features may be shown in somewhatschematic form. Features that are described and/or illustrated withrespect to one embodiment may be used in the same way or in a similarway in one or more other embodiments and/or in combination with orinstead of the features of the other embodiments.

Various aspects of the invention are similar to those described inInternational Patent Pub. No. WO2012045050; U.S. Pat. Nos. 8,140,168;7,865,245; 7,774,069; 7,711,433; 7,650,187; 7,571,007; 7,741,734;7,825,543; 6,591,139; 6,553,263; and 5,350,413; and U.S. Pub. Nos.2010/0308939; 2008/027293; and 2010/0102639, the entire contents ofwhich patents and applications are incorporated herein for all purposes.

Wireless Power Transmission System

Power may be transmitted wirelessly by magnetic induction. In variousembodiments, the transmitter and receiver are closely coupled.

In some cases “closely coupled” or “close coupling” refers to a systemthat requires the coils to be very near each other in order to operate.In some cases “loosely coupled” or “loose coupling” refers to a systemconfigured to operate when the coils have a significant spatial and/oraxial separation, and in some cases up to distance equal to or less thanthe diameter of the larger of the coils. In some cases, “looselycoupled” or “loose coupling” refers a system that is relativelyinsensitive to changes in physical separation and/or orientation of thereceiver and transmitter.

In various embodiments, the transmitter and receiver are non-resonantcoils. For example, a change in current in one coil induces a changingmagnetic field. The second coil within the magnetic field picks up themagnetic flux, which in turn induces a current in the second coil. Anexample of a closely coupled system with non-resonant coils is describedin International Pub. No. WO2000/074747, incorporated herein for allpurposes by reference. A conventional transformer is another example ofa closely coupled, non-resonant system. In various embodiments, thetransmitter and receiver are resonant coils. For example, one or both ofthe coils is connected to a tuning capacitor or other means forcontrolling the frequency in the respective coil. An example of closelycoupled system with resonant coils is described in International Pub.Nos. WO2001/037926; WO2012/087807; WO2012/087811; WO2012/087816;WO2012/087819; WO2010/030378; and WO2012/056365, and U.S. Pub. No.2003/0171792, incorporated herein for all purposes by reference.

In various embodiments, the transmitter and receiver are looselycoupled. For example, the transmitter can resonate to propagate magneticflux that is picked up by the receiver at relatively great distances. Insome cases energy can be transmitted over several meters. In a looselycoupled system power transfer may not necessarily depend on a criticaldistance. Rather, the system may be able to accommodate changes to thecoupling coefficient between the transmitter and receiver. An example ofa loosely coupled system is described in International Pub. No.WO2012/045050, incorporated herein for all purposes by reference.

Power may be transmitted wirelessly by radiating energy. In variousembodiments, the system comprises antennas. The antennas may be resonantor non-resonant. For example, non-resonant antennas may radiateelectromagnetic waves to create a field. The field can be near field orfar field. The field can be directional. Generally far field has greaterrange but a lower power transfer rate. An example of such a system forradiating energy with resonators is described in International Pub. No.WO2010/089354, incorporated herein for all purposes by reference. Anexample of such a non-resonant system is described in International Pub.No. WO2009/018271, incorporated herein for all purposes by reference.Instead of antenna, the system may comprise a high energy light sourcesuch as a laser. The system can be configured so photons carryelectromagnetic energy in a spatially restricted, direct, coherent pathfrom a transmission point to a receiving point. An example of such asystem is described in International Pub. No. WO2010/089354,incorporated herein for all purposes by reference.

Power may also be transmitted by taking advantage of the material ormedium through which the energy passes. For example, volume conductioninvolves transmitting electrical energy through tissue between atransmitting point and a receiving point. An example of such a system isdescribed in International Pub. No. WO2008/066941, incorporated hereinfor all purposes by reference.

Power may also be transferred using a capacitor charging technique. Thesystem can be resonant or non-resonant. Exemplars of capacitor chargingfor wireless energy transfer are described in International Pub. No.WO2012/056365, incorporated herein for all purposes by reference.

The system in accordance with various aspects of the invention will nowbe described in connection with a system for wireless energy transfer bymagnetic induction. The exemplary system utilizes resonant powertransfer. The system works by transmitting power between the twoinductively coupled coils. In contrast to a transformer, however, theexemplary coils are not coupled together closely. A transformergenerally requires the coils to be aligned and positioned directlyadjacent each other. The exemplary system accommodates looser couplingof the coils.

While described in terms of one receiver coil and one transmitter coil,one will appreciate from the description herein that the system may usetwo or more receiver coils and two or more transmitter coils. Forexample, the transmitter may be configured with two coils—a first coilto resonate flux and a second coil to excite the first coil. One willfurther appreciate from the description herein that usage of “resonator”and “coil” may be used somewhat interchangeably. In various respects,“resonator” refers to a coil and a capacitor connected together.

In accordance with various embodiments of this disclosure, the systemcomprises one or more transmitters configured to transmit powerwirelessly to one or more receivers. In various embodiments, the systemincludes a transmitter and more than one receiver in a multiplexedarrangement. A frequency generator may be electrically coupled to thetransmitter to drive the transmitter to transmit power at a particularfrequency or range of frequencies. The frequency generator can include avoltage controlled oscillator and one or more switchable arrays ofcapacitors, a voltage controlled oscillator and one or more varactors, aphase-locked-loop, a direct digital synthesizer, or combinationsthereof. The transmitter can be configured to transmit power at multiplefrequencies simultaneously. The frequency generator can include two ormore phase-locked-loops electrically coupled to a common referenceoscillator, two or more independent voltage controlled oscillators, orcombinations thereof. The transmitter can be arranged to simultaneouslydelivery power to multiple receivers at a common frequency.

In various embodiments, the transmitter is configured to transmit a lowpower signal at a particular frequency. The transmitter may transmit thelow power signal for a particular time and/or interval. In variousembodiments, the transmitter is configured to transmit a high powersignal wirelessly at a particular frequency. The transmitter maytransmit the high power signal for a particular time and/or interval.

In various embodiments, the receiver includes a frequency selectionmechanism electrically coupled to the receiver coil and arranged toallow the resonator to change a frequency or a range of frequencies thatthe receiver can receive. The frequency selection mechanism can includea switchable array of discrete capacitors, a variable capacitance, oneor more inductors electrically coupled to the receiving antenna,additional turns of a coil of the receiving antenna, or combinationsthereof.

In general, most of the flux from the transmitter coil does not reachthe receiver coil. The amount of flux generated by the transmitter coilthat reaches the receiver coil is described by “k” and referred to asthe “coupling coefficient.”

In various embodiments, the system is configured to maintain a value ofk in the range of between about 0.2 to about 0.01. In variousembodiments, the system is configured to maintain a value of k of atleast 0.01, at least 0.02, at least 0.03, at least 0.04, at least 0.05,at least 0.1, or at least 0.15.

In various embodiments, the coils are physically separated. In variousembodiments, the separation is greater than a thickness of the receivercoil. In various embodiments, the separation distance is equal to orless than the diameter of the larger of the receiver and transmittercoil.

Because most of the flux does not reach the receiver, the transmittercoil must generate a much larger field than what is coupled to thereceiver. In various embodiments, this is accomplished by configuringthe transmitter with a large number of amp-turns in the coil.

Since only the flux coupled to the receiver gets coupled to a real load,most of the energy in the field is reactive. The current in the coil canbe sustained with a capacitor connected to the coil to create aresonator. The power source thus only needs to supply the energyabsorbed by the receiver. The resonant capacitor maintains the excessflux that is not coupled to the receiver.

In various embodiments, the impedance of the receiver is matched to thetransmitter. This allows efficient transfer of energy out of thereceiver. In this case the receiver coil may not need to have a resonantcapacitor.

Turning now to FIG. 1, a simplified circuit for wireless energytransmission is shown. The exemplary system shows a series connection,but the system can be connected as either series or parallel on eitherthe transmitter or receiver side.

The exemplary transmitter includes a coil Lx connected to a power sourceVs by a capacitor Cx. The exemplary receiver includes a coil Lyconnected to a load by a capacitor Cy. Capacitor Cx may be configured tomake Lx resonate at a desired frequency. Capacitance Cx of thetransmitter coil may be defined by its geometry. Inductors Lx and Ly areconnected by coupling coefficient k. Mxy is the mutual inductancebetween the two coils. The mutual inductance, Mxy, is related tocoupling coefficient, k.Mxy=k√{square root over (Lx·Ly)}

In the exemplary system a power source Vs can be in series with atransmitter coil Lx so it may have to carry all the reactive current.This puts a larger burden on the current rating of the power source andany resistance in the source will add to losses.

The exemplary system includes a receiver configured to receive energywirelessly transmitted by the transmitter. The exemplary receiver isconnected to a load. The receiver and load may be connected electricallywith a controllable switch.

In various embodiments, the receiver includes a circuit elementconfigured to be connected or disconnected from the receiver coil by anelectronically controllable switch. The electrical coupling can includeboth a serial and parallel arrangement. The circuit element can includea resistor, capacitor, inductor, lengths of an antenna structure, orcombinations thereof. The system can be configured such that power istransmitted by the transmitter and can be received by the receiver inpredetermined time increments.

In various embodiments, the transmitter coil and/or the receiver coil isa substantially two-dimensional structure. In various embodiments, thetransmitter coil may be coupled to a transmitter impedance-matchingstructure. Similarly, the receiver coil may be coupled to a receiverimpedance-matching structure. Examples of suitable impedance-matchingstructures include, but are not limited to, a coil, a loop, atransformer, and/or any impedance-matching network. Animpedance-matching network may include inductors or capacitorsconfigured to connect a signal source to the resonator structure.

In various embodiments, the transmitter is controlled by a controller(as shown in FIG. 1) and driving circuit. The controller and/or drivingcircuit may include a directional coupler, a signal generator, and/or anamplifier. The controller may be configured to adjust the transmitterfrequency or amplifier gain to compensate for changes to the couplingbetween the receiver and transmitter.

In various embodiments, the transmitter coil is connected to animpedance-matched coil loop. The loop is connected to a power source andis configured to excite the transmitter coil. The first coil loop mayhave finite output impedance. A signal generator output may be amplifiedand fed to the transmitter coil. In use power is transferredmagnetically between the first coil loop and the main transmitter coil,which in turns transmits flux to the receiver. Energy received by thereceiver coil is delivered by Ohmic connection to the load.

One of the challenges to a practical circuit is how to get energy in andout of the resonators. Simply putting the power source and load inseries or parallel with the resonators is difficult because of thevoltage and current required. In various embodiments, the system isconfigured to achieve an approximate energy balance by analyzing thesystem characteristics, estimating voltages and currents involved, andcontrolling circuit elements to deliver the power needed by thereceiver.

In an exemplary embodiment, the system load power, P_(L), is assumed tobe 15 Watts and the operating frequency, f, is 250 kHz. Then, for eachcycle the load removes a certain amount of energy from the resonance:

$e_{L} = {\frac{P_{L}}{f} = {60\mspace{14mu} µ\; J\mspace{14mu}{Energy}\mspace{14mu}{the}\mspace{14mu}{load}\mspace{14mu}{removes}\mspace{14mu}{in}\mspace{14mu}{one}\mspace{14mu}{cycle}}}$

It has been found that the energy in the receiver resonance is typicallyseveral times larger than the energy removed by the load for operative,implantable medical devices. In various embodiments, the system assumesa ratio 7:1 for energy at the receiver versus the load removed. Underthis assumption, the instantaneous energy in the exemplary receiverresonance is 420 μJ.

The exemplary circuit was analyzed and the self inductance of thereceiver coil was found to be 60 uH. From the energy and the inductance,the voltage and current in the resonator could be calculated.

$e_{y} = {\frac{1}{2}{Li}^{2}}$$i_{y} = {\sqrt{\frac{2e_{y}}{L}} = {3.74\mspace{14mu} A\mspace{14mu}{peak}}}$v_(y) = ω L_(y)i_(y) = 352  V  peak

The voltage and current can be traded off against each other. Theinductor may couple the same amount of flux regardless of the number ofturns. The Amp-turns of the coil needs to stay the same in this example,so more turns means the current is reduced. The coil voltage, however,will need to increase. Likewise, the voltage can be reduced at theexpense of a higher current. The transmitter coil needs to have muchmore flux. The transmitter flux is related to the receiver flux by thecoupling coefficient. Accordingly, the energy in the field from thetransmitter coil is scaled by k.

$e_{x} = \frac{e_{y}}{k}$

Given that k is 0.05:

$e_{x} = {\frac{420\mspace{14mu} µ\; J}{0.05} = {8.4\mspace{14mu}{mJ}}}$

For the same circuit the self inductance of the transmitter coil was 146uH as mentioned above. This results in:

$i_{x} = {\sqrt{\frac{2\; e_{x}}{L}} = {10.7\mspace{14mu} A\mspace{14mu}{peak}}}$v_(x) = ω L_(x)i_(x) = 2460  V  peak

One can appreciate from this example, the competing factors and how tobalance voltage, current, and inductance to suit the circumstance andachieve the desired outcome. Like the receiver, the voltage and currentcan be traded off against each other. In this example, the voltages andcurrents in the system are relatively high. One can adjust the tuning tolower the voltage and/or current at the receiver if the load is lower.

Estimation of Coupling Coefficient and Mutual Inductance

As explained above, the coupling coefficient, k, may be useful for anumber of reasons. In one example, the coupling coefficient can be usedto understand the arrangement of the coils relative to each other sotuning adjustments can be made to ensure adequate performance. If thereceiver coil moves away from the transmitter coil, the mutualinductance will decrease, and ceteris paribus, less power will betransferred. In various embodiments, the system is configured to maketuning adjustments to compensate for the drop in coupling efficiency.

The exemplary system described above often has imperfect information.For various reasons as would be understood by one of skill in the art,the system does not collect data for all parameters. Moreover, becauseof the physical gap between coils and without an external means ofcommunications between the two resonators, the transmitter may haveinformation that the receiver does not have and vice versa. Theselimitations make it difficult to directly measure and derive thecoupling coefficient, k, in real time.

Described below are several principles for estimating the couplingcoefficient, k, for two coils of a given geometry. The approaches maymake use of techniques such as Biot-Savart calculations or finiteelement methods. Certain assumptions and generalizations, based on howthe coils interact in specific orientations, are made for the sake ofsimplicity of understanding. From an electric circuit point of view, allthe physical geometry permutations can generally lead to the couplingcoefficient.

If two coils are arranged so they are in the same plane, with one coilcircumscribing the other, then the coupling coefficient can be estimatedto be roughly proportional to the ratio of the area of the two coils.This assumes the flux generated by coil 1 is roughly uniform over thearea it encloses as shown in FIG. 2.

If the coils are out of alignment such that the coils are at a relativeangle, the coupling coefficient will decrease. The amount of thedecrease is estimated to be about equal to the cosine of the angle asshown in FIG. 3A. If the coils are orthogonal to each other such thattheta (A) is 90 degrees, the flux will not be received by the receiverand the coupling coefficient will be zero.

If the coils are arraigned such that half the flux from one coil is inone direction and the other half is in the other direction, the fluxcancels out and the coupling coefficient is zero, as shown in FIG. 3B.

A final principle relies on symmetry of the coils. The couplingcoefficient and mutual inductance from one coil to the other is assumedto be the same regardless of which coil is being energized.M_(xy)=M_(yx)

As described above, a typical TET system can be subdivided into twoparts, the transmitter and the receiver. Control and tuning may or maynot operate on the two parts independently. For example, as shown inFIG. 1, the transmitter or the receiver or both may include acontroller. The goal of this invention is to minimize the effect ofrelative spatial position and orientation on the magnetic field powertransfer rate between a transmitter and a receiver.

According to one embodiment, a TET system can include a set oftransmitter coils and a set of receiver coils. The number of coilswithin each set can be as few as one, however, if there is only onereceiver coil there must be at least two transmitter coils, and if thereis only one transmitter coil there must be at least two receiver coils.Thus, at least one of the receiver or the transmitter must have morethan one coil.

This invention modifies the existing components of a magnetic powertransmission system, specifically it introduces phased arrays oftransmitter coils and/or phased arrays of receiver coils. By utilizinginformation transmitted back from the receiver to the transmitter, thesystem can guarantee that a maximum magnetic flux reaches the receivercoils for a given geometry. This allows for more flexibility in thespatial arrangement between the transmitter and receiver by maintaininga more constant rate of power transfer than presently exists withexisting systems. Various aspects of the invention are directed togrouping of a plurality of coils and structures and methods for drivingand/or controlling the coils.

FIG. 4 shows an example of a transmitter 400 of a TET system withmultiple transmit coils 402, 404, 406, and 408. The transmit coils canbe equally sized and placed, for example, in the square arrangementshown in FIG. 4. Also shown in FIG. 4 is a receiver coil 410 placedadjacent to the transmit coils in a random position and orientation withrespect to the transmit coils. As described above and referencing FIG.1, each transmit coil can include an inductor Lx and can be connected toa power source Vs by a capacitor Cx. The receive coil can also includean inductor Ly connected to a load by a capacitor Cy. Capacitor Cx maybe configured to make Lx resonate at a desired frequency.

The coils can be driven by independent, but synchronized, drivercircuits, or they can be driven by a single common circuit, such asthose described below. In some embodiments, pairs of transmit coils canbe driven by a single circuit.

In one embodiment, shown in FIG. 5A, the transmit resonators 402, 404,406, and 408 can be arranged “in phase”, which has the equivalent effectof a large single coil. In a second embodiment, shown in FIG. 5B, two ofthe resonators can be arranged out-of-phase (first symmetry axis) withrespect to the remaining two coils. In a third embodiment, shown in FIG.5C, two of the coils are out-of-phase (second symmetry axis) withrespect to the remaining two coils.

Multiple transmitter coil control systems can be based on a singletransmitter circuit. FIG. 6 illustrates a basic TET system 600,including a transmitter 602 and a receiver 604. The transmitter 602 caninclude a voltage source V_(S), which can be a variable voltage, fixedor variable frequency voltage source. A driver circuit of thetransmitter 602 can include a resistor R_(S), a capacitor C_(S)(optional) and an inductor L_(S). The single transmitter coil orresonator L_(X) of transmitter 602 can comprise a pair of resistorsR_(X1) and R_(X2), a pair of capacitors C_(X1) and C_(X2), and aninductor L_(X). Capacitor C_(X2) can be variable to compensate forchanges in mutual inductance, M_(XY), between the transmitter and thereceiver. The driver circuit can be configured to excite the primary orsingle transmitter coil. The receiver 604 can include a receiver coilhaving a pair of resistors R_(Y1) and R_(Y2), a pair of capacitorsC_(Y1) and C_(Y2), and an inductor L_(Y). The load of the receiver cancomprise a resistor R_(L), a capacitor C_(L), and an inductor L_(L). Insome embodiments, capacitor C_(Y2) can be variable to compensate forchanges in M_(XY). The mutual inductance jωM_(XY) between L_(X) andL_(Y) is shown in both transmitter 602 and receiver 604 of FIG. 6.

FIG. 7 illustrates a transmitter 702 in which the transmitter includestwo transmit resonators L₁ and L₂. As shown, this circuit is amodification of the circuit described above in FIG. 6 which has only asingle transmit coil. Transmitter 702 includes many of the samecomponents described above, including voltage source V_(S), resistorsR_(S), R_(X1), and R_(X2), capacitors C_(S), C_(X1), and C_(X2),inductors L_(S) and L₁. Additionally, the transmitter can include asecond transmit coil, inductor L₂. As described above, the transmittercan comprise driver circuitry, as shown, configured to excite theprimary circuitry including the transmit coils. In embodiments where thecoils are operated out of phase, an additional capacitor C_(A) can becoupled to the inductor L₂, as shown. This additional capacitor canfunction to reduce primary capacitance when the coils operate out ofphase. When the transmitter resonators operate in phase, the mutualinductance between the transmitter and receiver can be represented asjω(M_(XY)−2M₁₂). When the transmitter resonators operate out of phase,the mutual inductance between the transmitter and the receiver can berepresented as jω(M_(XY)+2M₁₂).

Without C_(A), the circuit compensation would have to be done entirelyby the variable capacitance C_(X2), requiring a much larger variablerange of C_(X2). A larger range of C_(X2) is disadvantageous because ofincreased cost, more difficult circuit control, and lower precision inthe circuit compensation that in turn leads to an overall lower powertransfer efficiency.

With multiple transmitter coils there is a mutual inductance not onlybetween each transmitter coil and the receiver coil, but between eachpair of transmitter coils. With two transmitter coils, we can call thelatter M₁₂. Switching phase on a transmitter coil causes a sign changeon the M₁₂-induced voltage. This is equivalent of thinking of bothtransmitter coils as a system with a single self-inductance, and sayingthat the self-inductance is changed. As a result, the primary circuitcapacitance has to be adjusted, or else the eigen frequency LC may bewrong.

FIG. 8 illustrates an example of a transmitter 500 having four transmitcoils or resonators, L₁, L₂, L₃, and L₄. The transmitter can alsoinclude controller circuitry (not shown), as shown and described abovein FIG. 1. Although this specific embodiment is illustrated with fourtransmit coils, it should be understood that any number of resonatorscan be implemented using the same principles. The transmitter 500 caninclude at least one voltage source V_(S), which can be a variablevoltage, fixed or variable frequency voltage source. A driver circuit502 of the transmitter can include a resistor R_(S), a capacitor C_(S)(optional) and an inductor L_(S). A primary circuit 504 of thetransmitter having four transmitter resonators can comprise a pair ofresistors R_(X1) and R_(X2), a pair of capacitors C_(X1) and C_(X2), anoptional capacitor C_(A), and four inductors L₁, L₂, L₃, and L₄. Thedriver circuit can be configured to excite the primary transmitter coil.As described above, the transmitter can comprise driver circuitry, asshown, configured to excite the primary circuitry including the transmitcoils.

If all four coils are placed symmetrically, only a single capacitorC_(A) is required to compensate for mutual inductance changes whenoperating all coils in-phase or pair-wise out of phase. In thisembodiment, the transmitter system provides efficient power transferwithout a significant increase in complexity. Moreover, the number ofsystem options is increased significantly.

One will appreciate from the description herein that the coils can bemodified in a number of ways—number, position, and phase—to achieve adesired outcome. The system also provides a simple way to control themultiple transmission coils to achieve a greater number ofpossibilities. In some embodiments, multiple coil systems can comprisetwo coils placed in the same plane, four coils placed in a square arrayin the same plane, two coils at a 90 degree angle to each other, fourcoils arranged in pairs, with each pair at an angle to each other.Additionally, coils can be placed at angles of up to 120, 135, 150, etcdegrees to each other. In another embodiment, a large coil cancircumscribe a smaller coil in the same plane. In another embodiment,coils of the same or different size and same plane can be offset alongan axis. In one embodiment, pairs of coils can have the same size andsame normal vector, but offset along the axis and one pair rotated 90degrees around the axis. Additionally, in one embodiment there can be 2four coil arrays of the same size and orientation, but offset along anaxis.

The advantage of a multi-transmitter coil system is that the receivercan be located anywhere, and in any orientation, in the volume adjacentto either of the transmission coils. The use of a large transmissioncoil is both costly and cumbersome compared to the multiple smallercoils. The inventive system is also believed to be effective in a widerrange of situations, in part because the phases can be modified.

A TET system according to one embodiment can operate in two modes: atest mode and a power transmission mode. In its simplest configuration(see other configuration options below), there are several transmittercoils, but typically only one receiver coil.

Generally speaking, in the test mode, the transmitter system (such asthe transmitter of FIGS. 4-5) can operate one transmission resonator ata time, while the receiver measures the polarity (and optionally theamplitude and/or phase, see below) of the received magnetic flux. Thereceiver can measure the polarity and, optionally, the amplitude of themagnetic flux, with a controller or processor and additional sense andsignal processing circuitry located within the receiver. Thisinformation can be transmitted back to the transmitter controller. Theinformation measured or recorded by the receiver can then be processedand transmitted back to the transmitter controller. Communicationbetween the receiver and transmitter can be, for example, on a separatecommunications channel (not shown) or by transmitter modulation. Thisinformation can be telemetered by the same magnetic field coils, or byany other wireless technique, such as radio, including BlueTooth, WiFi,etc.

It is assumed the wavelength of the magnetic field is much larger thanthe characteristic dimensions of the transmitter and the receiver. Ifthis is not the case, the receiver needs to record phase informationduring the test mode, and each transmitter coil should be offset by itsphase lag during power transmission mode. In applications where theoperating frequency is hundreds of kilohertz (e.g., 250 kHz), thewavelength is at least hundreds of meter (1.2 km at 250 kHz), so fordevices no larger than a few meters, phase information is unnecessaryand coils should operate either in phase (0° phase) or out-of-phase(180° phase), as described.

Since power transmission in a TET system typically occurs at frequenciesof hundreds of kilohertz, the test mode can be completed on the order ofa few milliseconds, or even than one millisecond, even for up to 100separate transmitter coils, much faster than any realistic change of thegeometry. This means the geometry of the transmitter can be testedregularly, e.g., once a second, with no significant loss in powertransfer rate. It is also possible to configure the receiver to alertthe transmitter if the power transfer rate drops, and then begin a newtest mode.

In the power transmission mode, all transmission coils can operatesimultaneously, but can be divided into groups based on the polarity(plus or minus) of the received magnetic flux from each coil in the testmode. Thus, transmission of power from the transmitter resonators to thereceiver resonator can be adjusted based on the recorded polarities ofeach transmitter resonator from the test mode. The goal is to maximizethe amount of flux passing through the receiver resonator. But, flux inthe plus direction cancels out flux in the negative direction. As FIG.3B illustrates, there can be flux passing through the bottom to the topof a receiver then pass again through the top to the bottom. Thisresults in net zero energy. For an array of transmitter coils, they canhave a “plus” or “minus” polarity. If a receiver intercepts a “plus” and“minus” from its bottom, the energy cancels out to a net zero. But ifthe receiver intercepts a “plus” from its top and a “minus” from itsbottom, the energy adds up. In an environment where the implantedreceiver can assume a random orientation relative to the externaltransmitter, which itself can be wrapped around the patient's body,mixing transmitter polarities allows for more net energy to accumulatein the receiver.

For example, in a four coil transmitter system as shown in FIGS. 4-5,the coils can be divided into two groups of two transmitter coils. Inthe first group, all coils are operating in phase with each other (i.e.,the currents in all coils in this group are in phase). In the secondgroup, all coils are operating out-of-phase with the coils in the firstgroup.

In this configuration, the magnetic flux (and thus received electricpower) is maximized given the geometry of the system.

There are several possible permutations of the test mode. Any binarysearch algorithm can be used, i.e., any number of transmitter coilscould be powered at a time, as long as different combinations are testedin such a way as to deduce the appropriate polarity of each transmittercoil.

In one embodiment, to achieve maximum energy transfer the mastertransmitter controller can implement a process as follows (this is thebinary algorithm):

1. The controller turns on each individual transmitter, one at a time,for a specific amount of time. The controller then waits for thereceiver to send back information relating to the power received by eachtransmitter coil. This process can be used to determine which, if any ofthe transmitter coils transferred any power.

2. Next, the master controller can turn on the transmitter coils thatsuccessfully transferred power to the receiver, both with the samepolarity. The receiver can send back the amount of power received, andcompare that to the power originally received by the individual coils.

3. If the power received was less than originally received in 1. above,the master controller can adjust the polarity of the individualtransmitter coils. The receiver compares the amount of power received ineach iteration to previously received power levels until a maximum powerand ideal polarity configuration is identified.

The difference between this invention and existing solutions is thatthis invention guarantees the avoidance of zero power transfersituations, and it significantly improves the power transfer rate insituations where other solutions can only provide a marginal powertransfer rate. It can be cheaper to manufacture than exotically shapedreceiver coils. The disadvantages may be that the mass of thetransmitter increases, which means that there is a trade-off betweenmass and the power transfer improvements offered by this system when thetransmitter is carried by a person. Another potential disadvantage isthat some more control logic is needed by this system.

Utilizing an array of transmitter resonators allows for individuallyrigid resonators and electronics to be combined into a flexible arraythat may be worn by a person or made to conform to a surface. In thismanner, the coupling coefficient between the transmitting array and thereceiver resonator can be tailored by turning on, turning off, orreversing the polarity of current through the transmitting coils. Thisallows increased power transfer efficiency. Various arrays of flexiblyconnected rigid coils are shown in FIGS. 9A-9C.

FIG. 9A shows one embodiment of a transmitter 600 with four distinctcoil resonators, 602, 604, 606, and 608. In this embodiment, the coilscan be mounted onto a flexible fabric or substrate 610 (flexiblesubstrate shown). In some embodiments, the flexible substrate cancomprise Kapton or other polymide films, polyester films, or cloth, suchas cotton cloth. The individual resonators can be mounted to theflexible substrate or fabric and can be interconnected using a flexiblecircuit or discrete cabling 612 to allow communications between theresonators. The resonator can also include a connector 614 to anexternal power supply, for example. The transmit resonator can includeor be connected to all the other electrical components and circuitrydescribed above for operation in a TET system, including a controller,signal generator, power source, etc.

As shown in FIG. 9A, the coils are each connected to every other coilwith cabling 612, but it should be understood that the specificconnection patterns can vary (e.g., connecting the coils in series). Asthe flexible array conforms to a person's body or to an object used bythe person, the array utilizes an algorithm running on a controller, asmentioned elsewhere in this disclosure, to determine an optimalarrangement of coil polarities to maximize the power transfer or powertransfer efficiency to a separate receiver resonator.

FIG. 9B illustrates another embodiment of a transmitter 600 withmultiple rigid flexibly-connected coils. This particular embodiment cancomprise a 50 cm by 30 cm resonator made using 15 individual 10 cm by 10cm resonators. Each 10 cm by 10 cm resonator can be constructed on arigid surface, minimizing the wear and degradation of the wire coil andresonator electronics, but can be mounted on a flexible substrate orfabric (flexible fabric shown). As in the embodiment of FIG. 9A, theindividual resonators can be connected to each other with cabling orflexible circuitry.

FIG. 9C illustrates the transmitter 600 of FIG. 9A (or alternatively, ofFIG. 9B) conformably mounted to the body of a human patient. As shown inFIG. 9C, the flexible substrate or fabric upon which multiple individualcoils or resonators are mounted allows the resonator to conform to thebody of the patient. In doing so, the transmit resonator can moreeffectively transmit wireless power or energy to a receiver 601implanted within the body, which can be configured to deliver that poweror energy to another implanted medical device, such as heart pump 603.The conformability of the resonator 600 allows the multiple coils orresonators to more efficiently transfer power to the implanted receiver601 irrespective of the positioning or orientation of the receiverwithin the body. Since implanted devices can move or shift afterimplantation, the transmitter 600 of FIG. 9C advantageously compensatesfor shifts or movement of the implanted receiver.

When used in an environment with conductive metal surfaces, such as anoperating theater or hospital, magnetic shielding can be utilized tominimize the parasitic losses of the transmitter array. Nearbymoderately conductive objects comprised of steel, titanium, or similarmaterials act to both block the magnetic fields between the transmitterand receiver as well as dissipate the resonant energy as heat. Magneticshielding such as ferrite can be used with the transmitter to minimizethe effects of nearby parasitic objects, but materials such as ferriteare brittle. In one embodiment, a separate piece of ferrite can beplaced on individual resonators only. This can allow for the arrayitself to remain flexible. Another approach is to use malleable magneticmetals in conjunction with insulator strips to provide both magneticshielding and overall array flexibility.

Multiple coil systems according to this disclosure advantageously shapethe magnetic field to maximize the power transmitted to the receiver.The shaping is accomplished with coils of any shape, including simple,flat coils that are grouped to operate either in-phase or out-of-phasewith each other. This approach provides increased efficiency andreliability in situations where the receiver is not guaranteed to bestationary with respect to the transmitter, particularly in medicallyimplanted wireless power transfer systems.

These techniques have not been contemplated by others in the art sincemany wireless power transfer systems to date have required chargers forobjects such as cellular phones, consumer electronics, vehicles, etc,that remain stationary while charging. By contrast, for an implantablemedical application, a patient must be free to move around even whilethe implanted device is receiving power.

As described above, the magnetic flux in the receiver coil can bemaximized given the geometry of the system at the moment in time of thetest mode. If the geometry of the system is changing with time, e.g., ifthe receiver is moving or rotating with respect to the transmitter (suchas a person with an implanted receiver moving around in a bed with atransmitter below the mattress, or moving around a room or office with awall transmitter), or if the transmitter coils are moving with respectto each other (such as a person with an implanted receiver who wears agarment with transmitters, and this garment is worn slightly differentlyat different times, or if the garment moves in the wind), the system canrun the test mode again, to determine a new optimum grouping of thetransmission coils.

As an optional feature, the receiver can record the amplitude ofreceived magnetic flux (or received current, voltage, or power) duringthe test mode. This can be done in a situation where the system is notmaximizing the received magnetic flux, but rather maximizes the powertransfer ratio, i.e., in situations where power loss in the transmitteris an issue, such as when the transmitter is battery-powered instead ofconnected to wall power. By recording received magnetic flux amplitude,the system can choose to not power certain transmission coils in thepower transmission mode, namely all those coils which did not produce athreshold value of magnetic flux in the test mode. A higher thresholdvalue means a more power efficient system. A lower threshold value meansmore total power transmitted (down to zero threshold value, whichmaximizes the power transmitted as described above).

Note that the system could use, instead of just one receiver coil and anarray of transmitter coils, two or more receiver coils along with one ormore transmitter coils. In this case, during the test mode, eachtransmitter coil can be operated one at a time, while each receiver coilis operated one at a time, until all combinations are tested, andamplitude responses are recorded. Alternatively, any binary searchalgorithm can be used. Then, the best receiver coil (the coil with thelargest sum total of magnetic flux received) can be selected foroperation, and the transmitter coils grouped in-phase and out-of-phaseas described above. Finally, the other receiver coils are connected inphase with the first receiver coil (such that all receiver coilscontribute current to the receiver circuit in phase with each other).Just like what was described above, individual transmitter or receivercoils can be removed from the circuits if threshold values are notachieved.

The embodiments described herein do not depend on any particular shape,size, position, or orientation of transmitter or receiver coils. Coilsof different shapes and sizes are allowed, at arbitrary positions andorientations, including overlapping. The number of coils neededtypically is at least three (one receiver coil, two transmitter coils,or vice versa), but there is no upper limit to the number of coils thatcan be included in the system.

This disclosure can pertain to any device that receives power wirelesslyat a distance from the power source, including all types of electronics(cell phones, portable computers, PDAs, mobile games, remote controls,etc), electric cars, trains, and other vehicles, or any other devicethat uses electric power. The invention could be used to charge thebatteries of any such device, or to power it directly. The inventiondoes not rely on either the transmitter or receiver being in resonance,although it can take advantage of such systems.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the Claims appended hereto and theirequivalents.

What is claimed is:
 1. A wireless power transfer system, comprising: aflexible substrate adapted to conform to the body of a patient; a firsttransmitter resonator disposed on the flexible substrate; a secondtransmitter resonator disposed on the flexible substrate, the secondtransmitter resonator being in electronic communication with the firsttransmitter resonator; a receiver resonator; and a transmit controllerconfigured to drive the first and second transmitter resonators todeliver wireless energy to the receiver resonator, wherein the transmitcontroller is configured to operate in a test mode to drive the firsttransmitter resonator individually while a receive controller in thereceiver resonator is configured to record a polarity of the magneticflux received from the first transmitter resonator, and wherein thepolarity of the magnetic flux is defined by a direction in which themagnetic flux passes through the receiver resonator.
 2. The system ofclaim 1 wherein the flexible substrate comprises a flexible fabric. 3.The system of claim 1 wherein the flexible substrate is a materialselected from the group consisting of Kapton, a polymide film, apolyester film, a cloth, and a rubber.
 4. The system of claim 3, whereinthe flexible substrate is covered with a padding to better match acontour of the body.
 5. The system of claim 1 wherein the secondtransmitter resonator is driven out-of-phase from the first transmitterresonator.
 6. The system of claim 1 wherein the first and secondtransmitter resonators are rigid.
 7. The system of claim 1 wherein thetransmit controller is further configured to drive the secondtransmitter resonator individually while the receive controller in thereceiver resonator is configured to record a polarity of the magneticflux received from the second transmitter resonator.
 8. The system ofclaim 7 wherein the receive controller is configured to: detect adecrease in a power transfer rate between the first and secondtransmitter resonators and the receiver resonator; and transmit an alertto the transmit controller in response to detecting the decrease,wherein the alert causes the transmit controller to initiate a new testmode.
 9. The system of claim 1 wherein the receive controller isconfigured to communicate the measured polarity of the magnetic fluxreceived from the first transmitter resonator to the transmitcontroller, and the transmit controller is configured to adjusttransmission of power from the first transmitter resonator based on themeasured polarity.
 10. The system of claim 1, further comprising avariable capacitor electrically coupled to the first and secondtransmitter resonators to compensate for mutual inductance changes dueto changes in polarity of the first and second transmitter resonators.11. A method of adjusting wireless power transmission in a TET system,comprising the steps of: transmitting power from a first transmitterresonator external to a patient to a receiver resonator implanted withinthe patient; measuring a first polarity of magnetic flux received by thereceiver resonator from the first transmitter resonator, wherein thefirst polarity of the magnetic flux is defined by a direction in whichthe magnetic flux passes through the receiver resonator; transmittingpower from a second transmitter resonator external to the patient to thereceiver resonator implanted within the patient; measuring a secondpolarity of magnetic flux received by the receiver resonator from thesecond transmitter resonator, wherein the second polarity of themagnetic flux is defined by a direction in which the magnetic fluxpasses through the receiver resonator; communicating the measured firstand second polarities from the receiver resonator to a controller of thefirst and second transmitter resonators; and adjusting transmission ofpower from the first and second transmitter resonators based on themeasured first and second polarities.
 12. The method of claim 11,wherein the adjusting step comprises reversing a polarity of the firsttransmitter resonator.
 13. The method of claim 11, wherein the adjustingstep comprises reversing a polarity of the second transmitter resonator.14. The method of claim 11, wherein the adjusting step comprises turningoff the first transmitter resonator.
 15. The method of claim 11, whereinthe adjusting step comprises turning off the second transmitterresonator.
 16. The method of claim 11, wherein the adjusting stepcomprises adjusting a polarity of one or more of the first and secondtransmitter resonators to maximize power received by the receiverresonator.